Bone Tumour Radiology

Radiology of bone tumours is a recurring NEET PG favourite because a single radiograph, combined with patient age and lesion location, narrows the diagnosis dramatically. The plain film remains the single most important investigation; matrix, margin, periosteal reaction, and zone of transition are the four pillars you must read off every image.

How to approach a bone lesion (the diagnostic algorithm)

Before memorising eponyms, internalise the systematic reading order. NEET PG questions are almost always solvable by combining age + location + matrix + aggressiveness.

Age → Site within bone (epiphysis / metaphysis / diaphysis) → Site within skeleton → Margin & zone of transition → Matrix (osteoid / chondroid / ground-glass / lytic) → Periosteal reaction → Soft-tissue component

High-yield: Age is the single most discriminating factor. Under 1 year think metastatic neuroblastoma/infection; 1–20 years think Ewing's, osteosarcoma, simple bone cyst; 20–40 years think giant cell tumour (GCT); over 40 years think metastases, myeloma, chondrosarcoma.

Margin and zone of transition (Lodwick grading)

The zone of transition is the best single radiographic predictor of biological aggressiveness.

Lodwick type	Pattern	Zone of transition	Implication
IA	Geographic, sclerotic rim	Narrow	Benign, slow (e.g. NOF, simple bone cyst)
IB	Geographic, no sclerotic rim	Narrow	Benign but active
IC	Geographic, ill-defined margin	Wider	Locally aggressive (e.g. GCT)
II	Moth-eaten	Wide	Aggressive
III	Permeative	Imperceptible	Highly aggressive/malignant (Ewing's, lymphoma, infection)

High-yield: A narrow zone of transition = benign; a wide/permeative zone = aggressive/malignant. Permeative and moth-eaten patterns are the radiological hallmark of small round cell tumours and infection.

Matrix mineralisation

Matrix is the tumour's own intrinsic product seen as calcification/ossification.

Matrix type	Appearance	Tumours
Osteoid (bone-forming)	Cloud-like, ivory, fluffy, dense	Osteosarcoma, osteoblastoma, osteoid osteoma
Chondroid (cartilage)	Rings-and-arcs, popcorn, comma, stippled	Enchondroma, chondrosarcoma, chondroblastoma
Ground-glass / hazy	Smoky, smudged, "long lesion in a long bone"	Fibrous dysplasia
Fat	Lucent	Lipoma, intra-osseous lipoma
Lytic / no matrix	Pure lucency	GCT, simple bone cyst, ABC, metastases

High-yield: "Rings and arcs" or "popcorn" calcification = chondroid matrix (cartilage tumour). "Ground-glass" hazy matrix = fibrous dysplasia.

Periosteal reaction — the most examined sign

Periosteal reaction reflects how fast the lesion grows. Slow, continuous reaction = benign; interrupted, lamellated, spiculated = aggressive.

Periosteal reaction	Description	Classic association
Solid / buttressing	Thick, dense, uninterrupted	Benign (osteoid osteoma, fracture healing)
Onion-skin (lamellated)	Multiple concentric layers	Ewing's sarcoma (also osteomyelitis)
Sunburst / sunray spiculation	Radiating spicules perpendicular to cortex	Osteosarcoma
Hair-on-end	Fine perpendicular spicules	Skull in thalassaemia, sickle cell; also Ewing's
Codman's triangle	Elevated periosteum at lesion margin (no central reaction)	Osteosarcoma (also Ewing's, infection)

High-yield: Codman's triangle and sunburst/sunray pattern → osteosarcoma. Onion-skin (laminated) periosteal reaction → Ewing's sarcoma. Both Codman's triangle and onion-skinning are NON-specific (can occur in aggressive infection) but the classic NEET PG answers stand as above.

Primary bone tumours — system-wise

Osteosarcoma (osteogenic sarcoma)

The commonest primary malignant bone tumour (excluding marrow tumours like myeloma).

• Age: bimodal — peak 10–20 years; second peak >60 years (Paget's disease, post-radiation).
• Site: metaphysis of long bones; distal femur > proximal tibia > proximal humerus — i.e. around the knee (the most active growth plate).
• Radiology: mixed lytic-sclerotic lesion, cloud-like osteoid matrix, aggressive periosteal reaction — sunburst/sunray spiculation and Codman's triangle; wide zone of transition; soft-tissue mass.
• Spread: haematogenous → lungs (most common); "skip lesions" within the same bone are characteristic.
• Marker: raised serum alkaline phosphatase correlates with bulk and prognosis.
• Investigation of choice: plain radiograph for detection; MRI for local staging (marrow extent, skip lesions, neurovascular involvement); CT chest for metastases; bone scan/PET for skeletal spread. Biopsy confirms.
• Management: neoadjuvant chemotherapy → limb-salvage wide resection → adjuvant chemotherapy (MAP: high-dose Methotrexate, Adriamycin/doxorubicin, cisPlatin).

High-yield: Osteosarcoma "around the knee" with sunburst + Codman triangle is the single most repeated MSK radiology image. Telangiectatic osteosarcoma is purely lytic with fluid-fluid levels and mimics an aneurysmal bone cyst — distinguish by thick nodular enhancing septa.

Ewing's sarcoma

Small round blue cell tumour of children/adolescents.

• Age: 5–15 years (younger than osteosarcoma); rare >30 years.
• Site: diaphysis of long bones and flat bones (pelvis, ribs, scapula). (Classic teaching: diaphyseal; in practice often metadiaphyseal.)
• Radiology: permeative/moth-eaten lytic destruction, onion-skin (lamellated) periosteal reaction, large soft-tissue mass out of proportion to bony destruction. Codman's triangle and hair-on-end can also occur.
• Clinical mimic: fever, raised ESR/leukocytosis → mimics osteomyelitis.
• Genetics: t(11;22)(q24;q12) → EWS-FLI1 fusion; MIC2 (CD99) positive on immunohistochemistry.
• Investigation: radiograph + MRI for soft-tissue extent; biopsy with cytogenetics.
• Management: chemo-sensitive and radio-sensitive — multi-agent chemotherapy (VAC/IE: vincristine, adriamycin, cyclophosphamide, ifosfamide, etoposide) + local control by surgery/radiotherapy.

High-yield: Diaphyseal lytic lesion + onion-peel periosteum + large soft-tissue mass + fever in a child = Ewing's. Remember t(11;22) and CD99/MIC2.

Giant cell tumour (osteoclastoma)

Benign but locally aggressive; rarely metastasises to lung ("benign metastasising").

• Age: 20–40 years, only after physeal closure.
• Site: epiphysis/epimetaphysis extending to subchondral bone; distal femur, proximal tibia (around knee), distal radius.
• Radiology: eccentric, expansile, purely lytic lesion abutting the articular surface; "soap-bubble" appearance (multiloculated); narrow but non-sclerotic margin; cortical thinning.
• Histology: osteoclast-like multinucleate giant cells in a stroma of mononuclear cells (the neoplastic component).
• Management: extended intralesional curettage + adjuvant (phenol, cement/PMMA, cryotherapy); denosumab (RANKL inhibitor) for unresectable/recurrent disease.

High-yield: Eccentric, expansile, lytic, epiphyseal lesion reaching the joint surface in a 20–40-year-old with a soap-bubble look = GCT. The only common benign tumour reaching the articular surface in adults.

Fibrous dysplasia

Developmental anomaly — medullary bone replaced by fibro-osseous tissue.

• Radiology: "ground-glass" hazy matrix, lucent lesion with sclerotic rim ("rind sign"), "shepherd's crook" deformity of proximal femur, "long lesion in a long bone."
• Forms: monostotic (commonest) and polyostotic.
• McCune-Albright syndrome: polyostotic fibrous dysplasia + café-au-lait macules (coast of Maine, irregular borders) + precocious puberty; due to GNAS1 mutation.
• Mazabraud syndrome: fibrous dysplasia + intramuscular myxomas.

High-yield: Ground-glass matrix + shepherd's crook deformity = fibrous dysplasia. Café-au-lait with coast of Maine (irregular) = McCune-Albright; coast of California (smooth) = neurofibromatosis.

Osteoid osteoma vs osteoblastoma

Feature	Osteoid osteoma	Osteoblastoma
Nidus size	<1.5–2 cm	>2 cm
Site	Proximal femur, tibia; posterior spinal elements	Posterior elements of spine, long bones
Pain	Night pain, classically relieved by NSAIDs/aspirin	Less NSAID-responsive
Radiology	Lucent nidus + dense reactive sclerosis	Larger, more expansile, less sclerosis

High-yield: Painful scoliosis + night pain relieved by aspirin/NSAIDs in a teenager = osteoid osteoma (nidus on CT). The pain is prostaglandin-mediated. Treatment: CT-guided radiofrequency ablation.

Chondroid lesions

• Enchondroma: central lucent lesion with rings-and-arcs/stippled calcification; commonest tumour of the hand (phalanges). Ollier disease (multiple enchondromas) and Maffucci syndrome (enchondromas + soft-tissue haemangiomas) carry malignant transformation risk.
• Osteochondroma (exostosis): commonest benign bone tumour; metaphyseal bony outgrowth with cartilage cap, cortex and medulla continuous with parent bone, points away from joint. Cartilage cap >1.5–2 cm in adults suggests malignant transformation to chondrosarcoma.
• Chondroblastoma: epiphyseal lytic lesion in skeletally immature (younger than GCT); chicken-wire calcification.
• Chondrosarcoma: older adults (>40), axial skeleton/pelvis/proximal femur; chondroid matrix + endosteal scalloping + cortical destruction. Radio- and chemo-resistant → wide surgical excision is the mainstay.

High-yield: Osteochondroma is the only tumour with cortico-medullary continuity with the host bone — a giveaway image finding. Cartilage cap thickness predicts malignant change.

Cystic / lytic lesions

• Simple (unicameral) bone cyst: central, metaphyseal (proximal humerus/femur), in children; "fallen fragment sign" (fractured cortical fragment falls to the dependent part of the fluid-filled cyst).
• Aneurysmal bone cyst (ABC): eccentric, expansile, "blown-out", fluid-fluid levels on MRI/CT; often secondary to GCT/osteoblastoma.
• Non-ossifying fibroma (NOF)/fibrous cortical defect: eccentric, cortical, well-defined sclerotic rim; incidental in children, self-resolving.
• Brown tumour: lytic lesion of hyperparathyroidism (raised PTH, calcium); "osteitis fibrosa cystica."

High-yield: Fallen fragment sign = simple bone cyst; fluid-fluid levels = ABC (and telangiectatic osteosarcoma). Multiple lytic "punched-out" skull lesions in an elderly patient = multiple myeloma (cold on bone scan; skeletal survey/whole-body MRI preferred over bone scan).

Diaphyseal vs epiphyseal vs metaphyseal — a memory map

High-yield: Use location within the long bone as a fast filter.

• Epiphysis: GCT (after physeal closure), chondroblastoma (before closure), infection.
• Metaphysis: osteosarcoma, simple bone cyst, ABC, NOF, osteochondroma, chondromyxoid fibroma.
• Diaphysis: Ewing's sarcoma, adamantinoma, fibrous dysplasia, osteoid osteoma, lymphoma, Langerhans cell histiocytosis.

Mnemonic for diaphyseal lesions — "FEMALE": Fibrous dysplasia, Eosinophilic granuloma (LCH), Metastasis/Myeloma, Adamantinoma, Lymphoma, Ewing's.

Key differentials and discriminators

Confusion pair	Discriminator
Osteosarcoma vs Ewing's	Osteo: metaphysis, osteoid matrix, sunburst/Codman, 10–20 yr. Ewing: diaphysis, permeative, onion-skin, large soft-tissue mass, 5–15 yr, fever
GCT vs chondroblastoma	Both epiphyseal; GCT after physeal closure (20–40 yr), chondroblastoma before closure (<20 yr)
GCT vs ABC	GCT solid lytic, soap-bubble, reaches joint; ABC fluid-fluid levels, blown-out
Simple bone cyst vs ABC	SBC central + fallen fragment; ABC eccentric + fluid levels
Enchondroma vs bone infarct	Both calcify; infarct has serpiginous peripheral sclerotic rim, enchondroma has rings-and-arcs
Osteomyelitis vs Ewing's	Overlapping (permeative, onion-skin, fever); biopsy/culture decisive

Investigations — choice by scenario

• First-line / detection: plain radiograph (two views).
• Nidus localisation (osteoid osteoma): CT (best for cortical detail and nidus).
• Local staging / marrow & soft-tissue extent / skip lesions: MRI (investigation of choice for staging primary malignant bone tumours).
• Pulmonary metastases: CT chest.
• Skeletal spread: Tc-99m MDP bone scan (myeloma is an exception — often cold; use skeletal survey/whole-body MRI/PET).
• Definitive diagnosis: biopsy (must be along the planned resection tract; image-guided core biopsy preferred).

High-yield: MRI is best for marrow extent and skip lesions; CT is best for matrix mineralisation and cortical destruction; bone scan screens the whole skeleton (except myeloma).

Complications

• Pathological fracture (especially through lytic lesions and metastases).
• Malignant transformation: osteochondroma/enchondroma → chondrosarcoma; Paget's disease and fibrous dysplasia → osteosarcoma; chronic osteomyelitis sinus → Marjolin's ulcer (SCC).
• Pulmonary metastases (osteosarcoma, Ewing's).
• Local recurrence after curettage (GCT, ABC).
• Hypercalcaemia (myeloma, metastases), spinal cord compression (vertebral lesions).

Recently asked / exam angle

• Image-based single-best-answer: a radiograph "around the knee" with sunburst and Codman's triangle → osteosarcoma; identify the periosteal reaction by name.
• "Onion-peel/laminated periosteal reaction" → Ewing's sarcoma; linked second-order question on t(11;22) and CD99/MIC2.
• "Soap-bubble, eccentric, epiphyseal lytic lesion abutting joint surface in a 30-year-old" → GCT; treatment denosumab for unresectable disease.
• "Ground-glass matrix + shepherd's crook deformity" → fibrous dysplasia; café-au-lait coast of Maine vs coast of California distinction with McCune-Albright (GNAS1) vs NF-1.
• "Night pain relieved by NSAIDs + lucent nidus" → osteoid osteoma; RFA treatment.
• Matrix recognition: "rings-and-arcs/popcorn" = chondroid; identify chondrosarcoma's radio-resistance → surgery is treatment of choice.
• "Fallen fragment sign" vs "fluid-fluid levels" matching question (simple bone cyst vs ABC/telangiectatic osteosarcoma).
• Investigation of choice questions: MRI for local staging, CT chest for mets, why myeloma is cold on bone scan.
• Osteochondroma — the only lesion with cortico-medullary continuity; malignant transformation flagged by cartilage cap >2 cm.

Rapid revision

1. Age + location + matrix + zone of transition = the four keys to any bone tumour image.
2. Osteosarcoma: metaphysis around the knee, osteoid matrix, sunburst + Codman's triangle, lungs metastasis, raised ALP, MAP chemo.
3. Ewing's: diaphysis/flat bones, permeative, onion-skin, large soft-tissue mass, fever, t(11;22), CD99, chemo + radiotherapy sensitive.
4. GCT: epiphysis reaching joint, eccentric expansile soap-bubble lytic, 20–40 yr, denosumab for recurrence.
5. Fibrous dysplasia: ground-glass matrix, shepherd's crook; McCune-Albright = polyostotic FD + coast-of-Maine café-au-lait + precocious puberty (GNAS1).
6. Osteoid osteoma: <2 cm nidus, night pain relieved by NSAIDs/aspirin, CT-guided RFA.
7. Osteochondroma: only tumour with cortico-medullary continuity; cap >2 cm = malignant change; commonest benign tumour.
8. Enchondroma: rings-and-arcs, commonest tumour of the hand; Ollier/Maffucci risk malignancy.
9. Chondrosarcoma: older adults, axial; radio/chemo-resistant → wide excision.
10. Fallen fragment sign = simple bone cyst; fluid-fluid levels = ABC/telangiectatic osteosarcoma.
11. Narrow zone of transition = benign; permeative/moth-eaten = malignant or infection.
12. MRI = local staging/skip lesions; CT chest = pulmonary mets; myeloma is cold on bone scan (use skeletal survey/whole-body MRI).